Diamond abrasive



May 16, 1950 G. A. REHNBERG" DIAMOND ABRASIVE '4 Sheets-Sheet 1 FIG: 2.,

Filed Sept. 23, 1943 FIG.-1

IIIIIIII I I A GusTAF A. REHN BERG- y 1950 cs. A. REHNBERG 2,508,042

DIAMOND ABRASIVE Filed Sept. 25, 1943 4 Sheets-Sheet 2 FIG? FIG-8 FIGQ PM} 11 FIG: 10 I2 W m 50 y 1950 G. A. REHNBERG 2,508,042

nnmom: ABRASIVE Filed Sept. 23, 1943 4 Sheets-Sheet 3 FIG: 16

" FIG: 19

Pm 20 7s 76 I 46 m:-zW//////:///////% 30,, .67 [Ma ia GUSTAF \FZEHNBERG- y 1950 e. A. REHNBERG 2,508,042

01mm) ABRASIVE Filed Sept. 23, 1943 4 Sheets-Sheet 4 WW 99|N\\\ GUSTAF A. RE HN seize- Patented May 16, 1950 STATES PATENT OFFICE I DIAMOND ABRASIVE Application September 23, 1943, Serial No. 503,501

UNITED 7 Claims.

1 This invention relates to abrasives, and more particularly to abrasive articles such as grinding wheels utilizing diamond particles or grains as .the abradant.

. 2 that may be economically carried on in practice, for charging or loading a metal body such as the disk-like center of a grinding wheel with abrasive grain, particularly diamond grain. Other One object of the invention is to provide a objects will be in part obvious or in part pointed practical and eificient abrasive article in which out hereinafter. the abrasive grain is dependably carried for The invention accordingly consists in the feeabrasive action in a support such as metal, and tures of construction, combinations of elements, in the case of a grinding wheel, in a metal center arrangements of parts, and in the several steps which may be of sheet metal. Another object and relation and order of each of said steps to is to provide a grinding wheel, preferably utilizone or more of the others thereof, all as will be ing diamond abrasive, that can be efficiently and illustratively described herein, and the scope of reliably embodied in relatively thin construction, the application of which will be indicated in the as in a so-called cut-off wheel as may be employed following claims. for slicing or cutting quartz crystals. Another In the accompanying drawings in which are object is to provide a grinding wheel of the just shown a preferred embodiment of certain of the mentioned character that can utilize sheet metal mechanical features of my invention and also and that will have suitable strength or stiffness several illustrative embodiments of a grinding to dependably resist distortion out of its intended wheel construction, plane. Figure l is a plan view of a metal blank with Another object is to provide a metal grinding which to start the construction of a grinding wheel or abrasive article in which the portion of wheel; the metal part that carries the abrasive is in- Figure 2 is a cross section as seen along the tegral with the supporting portion, such as the line 2 2 of Figure 1; center in the case of a grinding e and can Figure 3 is a diametric cross-sectional view be given the desired degree of hardness or brittleshowing the blank of Figures 1 and 2 after the ness appropriate to eificient grinding, whether or performance thereon of a subsequent step; not the supporting portion of the metal has or Figure 4 is a central vertical sectional view is given analogous or similar qualities. Another showing certain dies and the blank of Figure 3 object is to provide a grinding wheel having a related to each other to perform a subsequent relatively thin sheet metal disk or center that ste will have dependable rigidity or strength or re- Figure 5 is a transverse diametrical section of sistance to distortion. Another object is to prothe blank as it appears after the dies of Figure 4 vide a sheet metal grinding wheel peripherally have operated upon it; carrying the abrasive grain that will have ade- Figure 6 is a plan view thereof showing one quate side clearance and that has structural charelement of peripheral slotting of the blank to acteristics to insure maintenance of such side prepare it for the reception of the abrasive parclearance during operation. Another object is ticles; in general to provide a diamond-charged metal Figure 7 is a fragmentary perspective view of grinding wheel of improved construction and a sheet metal strip coated for the reception of action. abrasive grain;

Another object is to provide a practical and Figure 8 is a transverse sectional view along efiicient method of constructing diamond-charged the line 88 of Figure '7; metallic abrasive articles. Another object is to Figure 9 is a similar transverse sectional view provide a practical and eflicient method of asshowing, however, the assemblage thereto 01 sembling abrasive grains, particularly diamond abrasive grains; grains, to a metal body or carrier such as a disk- Figure 10 is a transverse sectional view of the like center for a grinding wheel. Another obassemblage of Figure 9 as it appears after a subject is to provide an efficient and practical sequent operation to prepare it for compression; method for charging a metal body or carrier with Figure 11 is a vertical transverse sectional view abrasive grains, such as diamonds, and for giving that portion of the metal that directly carries the grains the desired characteristics for efficient grinding action. Another object is in general to provide an improved method, and one showing an illustrative construction of dies for compression of the assemblage of Figure 10;

Figure 12 is a vertical longitudinal sectional view as seen along the line I2i2 of Figure 11; Figure 13 is a perspective view showing the sheet metal and abrasive assemblage of Figure after operation thereon by the dies of Figures 11 and 12;

Figure 14 is a transverse sectional view along the line l4-l4 of Figure 13;

Figure 15 is a fragmentary side elevation on a larger scale of the blank of Figure 6 with certain parts assembled thereto;

Figure 16 is an edge view as seen along the line |6l5 of Figure 15;

Figure 17 is a fragmentary plan view, on an enlarged scale, of the blank of Figure 6 shown in relation to a fixture to illustrate a, possible modified method and construction for assembling abrasive grain thereto;

Figure 18 is a sectional view as seen along the line Iii-I8 of Figure 17;

Figure 19 is a diametrical vertical sectional view of the blank of Figure 15 or the blank of Figure 18 assembled to coacting dies for operating upon the metal of the blank and the abrasive grain;

Figure 20 is a fragmentary vertical sectional view, on an enlarged scale, as seen along substantially the line 20--20 of Figure 19;

Figure 21 is a fragmentary sectional view of the grinding wheel structure, showing the result thereon of the die operations performed by the dies of Figures 19 and 20;

Figure 22 is a diametric vertical sectional view showing the wheel structure of Figure 21 related to coacting dies for performing certain operations upon the sheet metal center or supporting portion thereof;

Figure 23 is a fragmentary vertical sectional view as seen along the line 23-23 of Figure 22, showing preferred or illustrative structures and features and relationships of the dies of Figure 22;

Figure 24 is a side elevation of the finished wheel, and

Figure 25 is a sectional view thereof as seen along the line 25-25 of Figure 24.

Similar reference characters refer to similar parts throughout the several views of the drawmgs.

I have selected for illustration of the various features of my invention a grinding wheel structure utilizing sheet steel and diamond abrasive grains but as is later pointed out, other sheet metals than steel may be employed and other abrasive grains than diamond may be used without departing from the spirit and scope of my invention. For greater ease and facility of initial working, I prefer to start with a relatively soft sheet metal which in the case of sheet steel may be cold rolled steel with a carbon content on the order of around 10% to 20% and hence being relatively soft and since my invention is also, particularly as to certain features thereof, best illustrated with respect to relatively thin wheels, the thickness of the sheet metal with which I may start may be on the order of 0.032". Out of such sheet metal I stamp a disk (Figures 1 and 2) of the desired diameter which in the selected illustrated embodiment is 8%" in diameter where I desire the ultimate wheel to be of an 8" diameter, and conveniently at the same time I may punch a round and coaxial hole 3| in the blank 30 to facilitate ultimate mounting of the wheel on a shaft or the like and this hole may be, for example, in diameter.

It will thus be noted that I prefer to start off with a disk of larger diameter than the ultimate diameter desired in order that, according to a preferred method, I may utilize the resultant surplus or excess metal to form a peripheral portion or rim, of suitable radial extent, that is of greater thickness than the remaining portion of the ultimate wheel, and also to achieve certain other advantages. Let it be assumed that the final or ultimate wheel, to be of 8" diameter as earlier noted, is to have a peripheral portion or rim of a thickness on the order of 0.045" in contrast to the initial sheet metal thickness of 0.032" and that the radial extent of the enlarged or thickened rim is to be on the order of The disk of Figure 2, being of 8%" diameter, I now shape, as by the use of suitable dies, to give it a cross section as shown in Figure 3, namely, to provide in what was the disk 30 of Figure 2 a peripheral flange 30a that makes an angle to the plane of the remaining portion 30b of about 45; the upturned flange 30a, extending at an angle of just about 45, is dimensioned so that the diameter of the resultant structure is 8", the flange 30a being virtually the hypotenuse of a right angle triangle each of whose legs is about 3 1" long, leaving the diameter of the portion 30b, which will hereinafter be referred to as the center 0r support," just about 7 /32".

I then provide companion dies like those shown in Figure 4 of which the lower one 3| comprises a bottom wall 32 surrounded by a cylindrical wall 33 whose inside diameter is just sufficient to receive therein the flanged structure of Figure 3, the diameter being accordingly, in the illustration, 8".

The upper face of the bottom wall 32 is shaped or machined to provide a flat circular face 34 of a diameter to just about match the diameter .of the center 30b of the structure of Figure 3,

hence about 7 /32", and extending about the circular face 34 is an annular recess or undercut 35 whose radial dimension is equal to the difference in the radii of the flange 30a and center 30b of Figure 3 and whose depth is about half the difference between the thickness of the rim portion of the ultimate wheel and the thickness of the sheet metal employed in making the stamping 30 of Figures 1, 2 and 3; illustratively the depth of the annular recess 35 could thus be one-half the difference between 0.05 and 0.032".

The flanged stamping of Figure 3 is inserted into the lower die 3| with the flange portion 30a directed upwardly and overlying the annular recess 35, substantially as shown in Figure 4, and thereafter the companion or upper die 36 is brought into action upon the inserted flanged sheet metal element.

The upper die comprises primarily a cylindrical member 31, diameter to be snugly received or telescoped into the lower die 3|, and its under face is provided with a downwardly projecting annular portion 38 of a radial dimension just about equal to the radial dimension of the annular recess 35 in the lower die 3| and in the illustration that dimension is /3z".

With the flanged blank inserted as above described, the dies 3| and 38 are now moved one toward the otherto bring the die parts 38 and 35 into action upon the metal of the upturned flange 30a; this may be done by any suitable means, such as a punch press, for example, but I prefer to achieve it by means of a suitable press such as an hydraulic press and hence I have indicated at 40 and II the lower and upper platens of such a press, with the lower die 3| resting upon the lower platen 40 and the upper platen II in engagement with the upper die 36 and just about to force the latter downwardly.

As the upper die 36 is thus forced downwardly,

and here it might be noted that when operating upon an 8" flanged blank otherwise dimensioned as above described, a pressure on the order of 200 tons may be employed, that svflicinrz to virtually cold-flow the metal of the flanged portion a downwardly into, and into conformity with, the annular die recess 35, the amount of metal in the flanged portion 30a being sufflcient in volume to provide a rim portion whose radial dimension equals that of the recess (being 3 1") and whose thickness is on the order of 0.045". This latter dimension is 0.013" greater than the initial sheet metal thickness of 0.032" and with the die recess 35 dimensioned to be, as above noted, of a depth equal to about one-half of 0.013", the resultant rim portion, shown at 300 in Figure 5, becomes symmetrically disposed with respect to a central plane,- indicated at A--A in Figure 5, through the sheet metal center 3017. The rim 300 thus projects laterally to the same extent from the two side faces of the center 30b, in each case by an amount on the order of 0.007" and, with the abrasive related to the thus thickened rim portion 300, the wheel is given substantial side clearance when used as a cut-off grinding wheel, such as for the cutting of quartz crystals.

Moreover, with the bottom face of die recess 35 and the under face of the upper die part 38 parallel, the side faces 42 and 43 of the thickened rim 300 of Figure 5 are also parallel and, of course, the outer face 44 of the rim 30c is a true cylinder, the metal of the upturned flange 30a in Figure 4 having been, under the substantial applied pressure, cold-flowed or conformed accurately and concisely to the corresponding surfaces of the die parts.

In the operation described in connection with Figure 4, there is no material flow or movement of metal from the flange 30a into the metal of the center 30b, such flow being resisted by the conformation of the center 30b itself and any tendency for such flow being counteracted by the provision of space, such as the die recess 35, into which flow can more easily take place and is in effect constrained thereto once a portion of the metal of flange 30a is brought down against and over the inner annular wall 39 of the die recess 35.

In the processing of the sheet metal blank as above described and with the metal of the blank initially relatively soft, the working of the metal such as shaping the blank of Figure 2 to give it the flange 30a of Figure 3, and more particularly the falling of the metal of the flange 30a into the conformation of the rim portion 300 of Figure 5, I have effected also such a working or re-arrangement of the molecules or fibrous structure of the metal as to harden it and even give it a substantial degree of brittleness and in the specific illustrative embodiment above described, the resultant hardness and brittleness is satisfactory and appropriate for functioning of the metal in good coaction with the abrasive grain ultimately to be assembled to it, as is later descrimd. If a lesser degree of hardness or brittleness is desired in the ultimate grinding wheel, I may anneal the structure, particularly the rim 300, to the desired extent.

In the rim 300 of Figure 5 I now mill or saw equi-distant spaced slots 46 which preferably extend substantially through the radial dimension of the rim 30c and while these slots may extend radially I prefer to cut them at an angle to corresponding radii of the wheel blank, somewhat as indicated in Figure 6, in order thereby to get a greater length or volume or capacity of slot within a given radial dimension of the rim 300. The slots 48 are preferably milled or sawed with the aid of any suitable indexing device and with a wheel blank of 8" diameter, as above assumed, I may provide, for example. 220 slots. The length or depth of the slots illustratively can be n g"- Into the slots I now proceed to embody abrasive grain. Bearing in mind the numerous slots per wheel and the magnitude of the task where wheels are to be produced in quantity, I prefer to provide structural features and a method to materially expedite the production of a wheel or wheels. According to my preferred method and construction, I first provide a strip of any suitable length and of appropriate cross section of a sheet metal having characteristics in general like those of copper and illustratively and preferably I employ sheet copper. A strip 4'! (Figure 7) of suitable length I bend along its center to give it a V-shaped cross section as indicated in Figure 8, finding an angle of bend of 90 convenient, and where the slots 46 are it" deep the initial width of the strip 41 is twice that dimension and its thickness may be on the order of 0.005". Onto the inside faces of the bent copper strip 41 I now apply a temporary binding material in substantially liquid form, such as shellac, and then sprinkle onto the she]- lacked surfaces of the two parts 41a and 41b of the strip 47, a quantity of abrasive grain such as diamond grain, of suitable grit size. Illustratively the grain can be of grit'size 60 Or finer and preferably is so screened that it includes smaller grains than the designated-grit size. Surplus grains are shaken off, leaving practically a single layer of grains, indicated at 50 in Figure 9 on the upper faces of the sheet metal member 41 as seen in Figure 9.

The two portions 41a and 41b are then folded or bent into substantial parallelism to each others bringing the two layers of grain 50 into contact with each other and resulting in a structural entity which in cross section appears somewhat as shown in Figure 10, the sheet metal element 4! being substantially U-shaped and having a vertical dimension just about equal to the depth of the slots 46 of the wheel blank of Figure 6. The grains 50 are dependably held within the folded sheet metal strip and the structure as above indicated can be of any desired length.

That structure is now operated upon to compress it and to make it separable into individual parts and this I preferably carry out by the use of coacting dies shown in Figures 11 and 12. They are of simple construction, comprising a lower die 5| provided with a longitudinal recess 52 of a width to receive the structure of Figure 10 whenlaid down on one of its sides, as shown in Figure 11, and a companion or upper die 53 which has projecting downwardly therefrom a die part 54 dimensioned to enter the lower die recess 52 but only to an extent to compress the assemblage 41-50 to a thickness just about equal to the thickness of the slots 46 in the wheel blank of Figure 6. Illustratively the width of the slots can be 0.020" and in such case the dies 5I--53 are constructed or operated always to compress the assemblage 4l50 to substantially the just stated dimension though preferably slightly less, for example, to a thickness of 0.019.

The bottom wall of the die recess 52 and the under face of the die part 54 are shaped to provide companion V-shaped or tooth-like projections 52a and 54a, as indicated in Figure 12, being regularly spaced lengthwise of the die parts 52 and 54 by distances that equal the axial dimension or thickness of the rim portion 300 as seen in Figure 5, being therefore in the illustrative embodiment spaced longitudinally by 0.045".

The dies and 53 of Figures 11 and 12 are preferably actuated by means of a suitable press such as a hydraulic press, the platens of which are indicated at 56 and 51, and in compressing the temporary assemblage 41-50 to a thickness on the order of 0.019, the metal of the sheet metal part 41 is in effect cold-flowed or forced into intimate inter-relation with, throughout and around all of the diamond grains 50, becoming as a result of the working of the metal hardened and somewhat friable or brittle, and securely bonding the grains 50 together by the resultant metal matrix. In Figure 13 is shown the product resulting from this compressing operation, being generally indicated by the reference character 58, and as indicated in Figure 13 some of the diamond grains 50 are visible through the outer surfaces of the metal and in the exagerated transverse sectional view thereof shown in Figure 14 there is indicated how the metal 59 of what was the sheet metal element 41 of Figures 7-12 is flowed and compacted about the grains 50 which are in effect uniformly distributed throughout the metal 59.

The companion V-shaped projections 52a and 54a will be seen from Figure 13 to form com panion indentations 66 in the bonded abrasive article 58, thus weakening the latter along its length and in effect marking the element 58 off into subdivisions 56a and thus making it possible easily to break the element 58 into individual smaller parts or to break it off piece by piece, but each individual part or piece thus broken off is dimensioned to be snugly received in a slot 46 of the wheel blank of Figure 6.

An element 58 of Figure 13 of any desired length is now used to fill up the slots 46 of the wheel blank and a convenient way of so doing is to insert the endmost marked off part 58a of the compacted rigid abrasive element 58 into a slot 46, utilizing the rest of the part 58 as a sort of handle to properly position the endmost part 58a in the selected slot 46 and also to force it into the slot into which it is received with a sort of friction fit, and then by simply swinging the rest of the bar or strip-like element 58 about the companion depressions 60-60 that mark off the selected or endmost part 58, simply break off the rest of the element 58, leaving what was the endmost part 58a properly seated in the slot 46. These steps are repeated for successive slots, thus using up as many prepared bonded abrasive strips 58 as are necessary. In Figures 15 and 16 is shown the wheel blank with bonded abrasive parts or blocks 58a set into the slots 46.

Insofar as other features of my invention are concerned, the slots 46 may, of course, be filled with abrasive grain in any other suitable manner, for example, with the aid of parts indicated in Figures 17 and 18. Thus I may provide any suitable fixture that has a flat bottom 62 against which may be laid the slotted blank of Figure 6 so that one of the side faces of the rim 30c rests flat against the bottom which is provided with a cylindrical side wall 63 that snugly encompasses the periphery of the wheel blank. In this manner the slots 46 may be closed 011 peripherally by the cylindrical side wall 63 and at one side opening thereof by the bottom wall 62,

leaving all of the slots open upwardly by way of their ends in the opposite face of the rim 300. The wall element 68 preferably projects upwardly beyond the rim 30c.

Into all of the slots 46 I then inject the abrasive grain preferably with a powdered metal like copper and conveniently a mixture of the grains, indicated at 50 in Figures 17 and 18, and of powdered metal, indicated at 64, is brushed into the slots to fill all of them and thereafter a temporary binder such as liquid shellac is applied, as by brushing over or into the filled slots. The temporary binder relatively quickly sets, as by evaporation therefrom of its vaporizable solvent, thus leaving the sheet metal wheel structure with all of its slots filled with a mixture of grain and powdered metal temporarily bonded together and held in the slots.

Having loaded the slots in the rim of the wheel blank, I now compact the metal of the thickened rim 300 against and virtually about the abrasive mix in the slots and, according to circumstances, effect an interlocking of the abrasive grain, or at least of some of them, with the metal of the rim 300. This I preferably accomplish by the use of companion dies constructed and coacting preferably as indicated in Figures 19 and 20; the dies comprise a lower die 65 and an upper die 66 constructed to be telescopically receivable one within the other and to operate upon the rim 300 of the interposed grinding wheel structure. Thus the lower die 65 may comprise a bottom portion 66 presenting a plane upper face 6! of a diameter on the order of the diameter of the wheel center 30b, surrounded by a raised annular portion 68 which in its upper face has cut into it grooves 10, as is better shown in cross section in Figure 20, which are upwardly concave and of a width somewhat greater than the width of the slots 46 in the rim 300; in the illustration the width of the slots is 0.020 and hence the width of the grooves 10 in the upper face of the die portion 68 may be on the order of, for example, two or more times the width of the abrasive slots 46. The slots 10 in the die part 68 are in number the same as the slots 46in the grinding wheel and they are similarly spaced and extend in the same relation to the radii as do the slots 46 in the rim 300. Accordingly with the abrasive-loaded wheel structure placed in the lower die 65, in which it is centered by the upstanding cylindrical side wall H, each loaded slot 46, as is better shown in Figure 20, overlies and is aligned with an upwardly concave groove 10 in the die part 68 while a substantial area of each rim part 30c (Fig. 20) that intervenes successive slots 46 rests flatwise against and is centered and aligned with the flat face 12 of the upstanding portion 13 of the die part 68 intervening two successive grooves 10.

The upper die 66 comprises a cylindrical element 14 that enters and is guided along the cylindrical wall H of the lower die 65 and in its under face it has projecting downwardly an annular portion 15 that is shaped or configured the same as is the die part 68 of the lower die 65. That is, it has downwardly concave grooves 16 aligned with and forming counterparts to the upwardly concave grooves I0 in the lower die part 68, successive grooves 16 being separated by downwardly projecting intervening portions 11 that are counterparts to the upwardly projecting portions 13 be of the lower die part 66.

eflect a flow of the metal of theintervening wheel parts "e (Figure 20) and in the case of an 8" wheel otherwise dimensioned as illustratively above described, a pressure on the order of from 300 to 400 tons is appropriate to flow the metal of the rim portions 80c into a cross sectional configuration substantially like that shown in Figure 21.

As indicated in Figure 21, the portions We of the wheel rim that intervene successive slots 46 are by the above described pressing operation thinned out somewhat throughout an extent corresponding to the registered or juxtaposed faces I2 and 18 of the die parts I8 and 13 respectively, the pressing operation having caused metal of the portions 30c to be displaced or flowed in opposite circumferential directions and respectively toward the two slots to either side of the portion 30c.

With this action taking place simultaneously upon the metal of each rim portion 362, each slot 46 is narrowed up and its contents tightly compressed therein, but due to the juxtaposed or mating grooves and 16 (see Figure 20) of the die members, some of the cold-flowed metal is guided by the curved walls of the die groove and moved laterally to each side of the wheel rim but still in a circumferential direction to narrow up and virtually close the slots 46 at the two sides of the wheel rim, as indicated in Figure 20 at 82. though the slots 46 are somewhat narrowed up in a circumferential direction, they are by the coldilowed metal also and at the same time substantially closed at the sides of the rim, but due to the manner in which the die parts guide the coldfiowing metal, there need not be any substantial increase in effective grinding rim thickness, that is, in the vertical dimension as viewed in Figure 21 of the now differently shaped and closed slot 46 or of the abrasive mass tightly compacted and encompassed therein. It will be noted that the flowed metal that effects side closure of the slots 46, indicated by the reference character 83 in Figure 21, assumes a progressively diminishing thickness, in effect tapering off to an exceedingly small dimension or thickness where it virtually meets, for slot-closing, a similarly conformed flowed metal portion ofthe next adjacent intervening rim part 38c. Moreover, this action is somewhat controllable according to the pressure exerted upon the dies 65, 66 of Figures 19 and 20 and that is preferably so controlled that the transverse dimension (the vertical dimension as seen in Figure 21) of the compacted abrasive portions is substantially 0.045", corresponding to the initial thickness produced in the rim 300 in the blank of Figure 5.

In the above described operation upon the metal of the rim, as in the die apparatus 65-66 of Figures 19 and 20, the resultant working of the metal to transform it from the conformation generally indicated in Figure 20 to the conformation indicated in Figure 21 effects a further hardening of the metal by re-arrangement of its molecular or fibrous structure and increased brittleness result. I have found that the resultant characteristics of the metal, are suitable and appropriate for coactlon during subsequent grinding operation of the wheel, the metal intervening the Thus abrasive-loaded slots progressively wearing or breaking away at a rate commensurate with the wear upon the abrasive grain 50 andwith the need for pressing new abrasive grains to the work being operated upon as grains wear down or break out of the mass contained in the individual slots 46. If less brittleness or other change in these characteristics of the metal are desired, the metal of the rim can be annealed.

' In the process of narrowing and closing up the slots as in Figure 21, some of the abrasive grains become more or less embedded in or enveloped by the cold-flowing metal of the wheel rim, thus insuring greater security of holding of the abrasive grains in place; this can be effected particularly with respect to such of the grains asare outermost or adjacent the outer boundaries of the compacted mass in each closed slot 46. Such action is facilitated even though the abrasive grains 50 are initially bonded together into a rigid, solid, compressed block such as a broken off part 58a of the structure 58 of Figure 13, for the metal 59 (Figure 14) thereof can yield sufliciently under the compression that takes place in the dies of Figure 19 to permit at least certain of the outermost grains to become embedded in or enveloped to a greater or less extent by the metal of the rim; in such case intermediate grains within the mass, and these are apt to be the smaller grains, remain relatively uniformly distributed throughout the cross section of the closed slots 46 and are held bonded by the metal 59 even though the latter is also made to flow and to become conformed to the changed cross section of the slots.

If a metal powder is intermingled with the abrasive grains as was described in connection with Figures 17 and 18, the mixture, bonded together and held in the slots by the temporary binder such as shellac, undergoes compression and compacting when the metal is cold-flowed as in Figure 21. Outermost grains can thereby also become more or less embedded in the metal of the walls of the closed slot, and the compacted metal powder can act during the compression to prevent crumbling or crushing of the grain, functioning to envelope and cushion and to help to hold assembled particularly those grains that are intermediate of the outermost grains as viewed in Figure 21.

In the course of the various operations such as those above described, and most of which are con fined to operations upon the thickened rim of the wheel or wheel blank, the wheel center 30b undergoes various strains and stresses, sometimes be comes warped or distorted out of its plane, and sometimes becomes in effect undulating in cross section; such factors have the effect of a weakened wheel center or abrasive rim support and frequently have the effect of making the abrasive rim run out-of-true. Also, the initial softness of the metal of the blank persists very materially and the center could, therefore, have a deficiency in rigidity. To overcome such and other possible defects or disadvantages, I next subject the otherwise finished grinding wheel to an operation in which I preferably employ companion dies to operate upon the wheel 30b and these may take the form shown in Figures 22 and 23.

The lower die 65 has a bottom wall 86 surrounded by an outer cylindrical wall 81 of an inside diameter to snugly receive and center the grinding wheel structure but the upper face of the bottom wall 86 is recessed or undercut as at 88 to provide an annular recess of adequate depth to accommodate the laterally projecting portions 1 l of the abrasive rim, leaving a. central circular face 89 of a diameter just about equal to the diameter of the wheel center 3% which thus rest flatwise thereagainst.

The companion or upper die 9| comprises a cylindrical die part 92 that enters into the lower die 85, being guided by the wall 81 of the latter, and it has an under circular face 93 of a diameter equal to that of the wheel center 3%, being peripherally cut away as at 94 to provide an annular recess to accommodate the upwardly projecting rim portions of the wheel inserted into the lower die 85.

The die faces 89 and 93, between which the wheel center 30b may be subjected to compression, are broken up preferably in a regular pattern but unsymmetrically with respect to the two faces themselves, and an illustrative construction comprises criss-crossing each of the two die faces 89 and 93 with slots S of suitable width, for example, T g" and suitably spaced so that each die face is broken up into squares T, separated from each other by the slots S, giving an effect analogous to that found in a waffle iron. In so slotting the two die faces which in operation are coaxial, the slots in the one are so displaced relative to the slots in the other that the square areas T in the one have their center points substantially aligned with the center points of slot intersections in the other, as is clearly shown in Figure 23.

With a wheel operatively related to the dies 85 and Bi as above described, the two dies are pressed one toward the other thus to subject the wheel center 30b to the action of the above described die faces 89 and 93, more particularly to their relatively staggered parts T and slots S, and this I preferably do by way of an hydraulic press the platens of which are indicated in Figure 22 at 95 and 96. With a wheel center dimensioned as above described for an 8" wheel, the pressure employed can be on the order of 200 tons.

As a result, the metal of the wheel center 30b is worked and here several actions take place. For example, what might be termed surplus of metal in the center 30b has caused it to assume a warped or undulatory configuration, is made in effect to flow into such regions of the center 30b as are not directly under compression, namely, into uncompressed regions intervening adjacent die portions T on either side. The slots S in the die faces and the relationship of the parts T thereof are thus enabled to straighten out the wheel center 30b and in effect restore it to a straight or flat condition free from curvature, undulation, warping or the like. Such cold-flow of metal and also the direct compression which certain areas receive, and they are uniformly distributed throughout the area of the wheel center 3012, effect such working of the metal of the center 30b as to make it considerably harder than it was initially, due to the re-arrangment of the molecular or fibrous structure of the metal, and thus the sheet metal center 30b is inherently made stiffer and more rigid and adequately so, even though relatively thin, to dependably support the abrasive rim during grinding operations.

That there is such actual cold-flow of metal in the wheel center 30b appears also from the finished product itself, as indicated in Figures 24 and 25, for in both faces of the center 30b can be seen and found square areas, corresponding to the parts T of the dies of Figures 22 and 23, that appear and are depressed in usually varying degrees according apparently as the amount of metal varied with the extent of undulating or curva- 12 ture prior to the straightening out and stiffening operation, and certain of such areas are indicated in Figures 24 and 25 by the reference character 97.

The wheel may now be mounted in any suitable way, as by making use of the central mounting hole 3|. For cutting off or slicing very hard substances such as quartz crystals, the wheel is found to be efficient and of good grinding and cutting characteristics, the thickened abrasive rim construction in coaction with the relatively thin but straight, strong and stiff center makes for the achievement of good side clearance during grinding and for dependable maintenance of such side clearance, for the structural features of the wheel center 3012 resist warping or the like and contribute toward straight-line cut-off action, a very material factor where precision is required as in the slicing of quartz crystals.

Other abrasive grain than diamonds may be employed, such as garnet, fused alumina, silicon carbide, etc., etc., and though I have chosen to illustrate my invention with respect to a sheet metal structure of steel, other metals than steel may be employed, such as cooper, aluminum, bronze, alloys, and the like, and it will be understood, in view of the foregoing description, that various factors above mentioned may be varied as may be necessary or desired according to the particular characteristics of the metal employed; thus, some metals may respond'to a greater or less extent than others to the hardening and other effects caused by the working or cold-flow of the metal and where necessary or desired control of the desired end results may be effected by appropriate application of annealing and to such extent as may be necessary or desired.

It will also now be understood that where a wheel of dimensions other than those illustratively above set forth is to be made, various factors may be correspondingly varied such as, for example, the dimensions of the upturned flange 30a in the blank of Figure 3 in relation to the ultimate rim thickness desired, the thickness of i the sheet metal initially employed, the radial extent of the thickened rim portion, and the like, and these factors may in turn be varied according to the particular characteristics of the metal or alloy to be used.

It will thus be seen that there has been provided by this invention an article in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawin s is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a method of forming an abrasive wheel the steps which comprise, forming a sheet metal disk of larger diameter than that of the ultimate wheel, bending an outer annular portion of said disk out of the plane of the remainder of said disk, compressing the said bent portion to form an annulus of lesser diameter than the initial diameter of said disk and of greater thickness than the remainder of said disk, and applying abrasive grain to the said annular portion.

2. In a method of forming an abrasive wheel the steps which comprise, forming a sheet metal disk of larger diameter than that of the ultimate wheel, bending an outer annular portion of said disk out of the plane of the remainder of said disk, compressing the said bent portion to form an annulus of lesser diameter than the initial diameter of said disk and of greater thickness than the remainder of said disk, applying abrasive grain to the said annular portion, and app ying forces of compression to the remainder of said disk, other than said annular portion of increased thickness, throughout distributed areas thereof to stifien said remainder of the disk by altering the physical characteristics of the metal thereof.

3. In a method of forming an abrasive Wheel the steps which comprise, forming a sheet metal disk of larger diameter than that of the ultimate wheel, bending an outer annular portion of said disk out of the plane of the remainder of said disk, compressing the said bent portion to form a solid metal annulus of greater thickness than the remainder of said disk and of lesser diameter than the initial diameter of the disk, thereby forming an annular rim that is integral with the remainder of the disk and that projects, because of said greater thickness, laterally beyond the faces of the remainder of the disk, incorporating abrasive material into said rim, and subjecting the remainder of the disk to pressure exerted at spaced intervals and so that the areas of pressure application to one surface of the remainder of said disk are intermediate and not aligned with the areas of application of pressure to the other surface of said remainder of said disk.

4. In a method of forming an abrasive wheel the steps which comprise forming a metal disk and cutting away the metal at spaced intervals to form spaced slots extending radially inward from the periphery of the disk, filling the slots with a mixture of metal powder bond and abrasive, and restricting the open sides of the slots by applying pressure to the metal laterally and in restricted regions intervening successive slots to flow metal in opposed circumferential directions from said regions and hence circumferentially toward each slot and by the resultant restriction of the lateral ends of the slots hold the slot fillings against lateral emergence from the slots.

5. In a method of forming an abrasive wheel the steps which comprise forming a metal disk and milling peripherally spaced slots extending radially inward from the periphery of the disk, depositing abrasive means in the slots, and laterally compressing substantially only central portions of the areas of metal intermediate of successive slots to displace and flow metal in opposite circumferential directions and respectively toward the lateral open sides of successive slots and thereby restrict said slots at the sides of the disk to hold the abrasive means therein against lateral displacement.

6. In a method of forming an abrasive wheel the steps which comprise forming a metal disk working an outer annular portion of said disk to strengthen it, forming recesses in said strengthened outer annular portion and filling said recesses with abrasive, and subjecting the center portion of said disk lying within said outer annular portion to compressive forces throughout individual and distributed areas thereof to straighten said portion and aid it to resist distortion.

7. In a method of forming an abrasive wheel, the steps which comprise pressure-working the metal of an outer annular portion of a sheet metal disk to materially reduce the radial dimension of said annular portion and to materially and uniformly increase the thickness thereof, whereby to provide an outer rim-like annulus of solid metal of greater thickness than said sheet metal, said rim-like annulus thereby projecting laterally beyond the sides of the rest of said disk which forms a supporting center for said annulus, forming slots at spaced intervals in said annulus, charging said slots with abrasive, restrict ing the open sides of the slots by applying pressure to the metal of the annulus in restricted regions intervening successive slots to flow metal in opposed circumferential directions from said regions and hence circumferentially toward each slot and by the resultant restriction of the sides of the slots hold the abrasive charges in the slots against emergence from the slots, and subjecting the sheet metal of said center to compression by forces applied thereto from opposite sides thereof and throughout individual distributed areas of each face of said center, which are displaced relative to each other, thereby to increase the hardness of the metal of the center and to straighten the latter out.

GUSTAF A. REHNBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 7 Date 172,337 Morrison Jan. 18, 1876 894,046 Peirce July 21, 1908 1,022,269 Meyers Apr. 9, 1912 1,063,380 Peirce June 3, 1913 1,989,074 Bullard Jan. 29, 1935 2,069,788 VanDerPyl Feb. 9, 1937 2,270,209 VanDerPyl Jan. 13, 1942 FOREIGN PATENTS Number Country Date 3,677 Great Britain Oct. 22, 1875 28,972 Great Britain 1911 288,625 Germany Nov. 11, 1915 542,054 Great Britain Dec. 23, 1941 655,234 France Dec. 17, 1928 

